Use calloc for sshkeys if mmap is not supported.

Based on Github PR#597 from Mike Frysinger, any bugs added by me.

Author: daztucker

configure.ac

@@ -536,6 +536,7 @@ AC_CHECK_HEADERS([ \
     nlist.h \
     poll.h \
     stdint.h \
+    sys/mmap.h \
     sys/stat.h \
     sys/time.h \
     sys/un.h \
@@ -2103,6 +2104,7 @@ AC_CHECK_FUNCS([ \
 	memmove \
 	memset_s \
 	mkdtemp \
+	mmap \
 	ngetaddrinfo \
 	nlist \
 	nsleep \

sshkey.c

@@ -723,6 +723,7 @@ sshkey_sk_cleanup(struct sshkey *k)
 static int
 sshkey_prekey_alloc(u_char **prekeyp, size_t len)
 {
+#if defined(HAVE_MMAP) && defined(MAP_ANON) && defined(MAP_PRIVATE)
 	u_char *prekey;
 
 	*prekeyp = NULL;
@@ -734,14 +735,21 @@ sshkey_prekey_alloc(u_char **prekeyp, size_t len)
 #endif
 	*prekeyp = prekey;
 	return 0;
+#else
+	*prekeyp = calloc(1, len);
+#endif /* HAVE_MMAP et al */
 }
 
 static void
 sshkey_prekey_free(void *prekey, size_t len)
 {
+#if defined(HAVE_MMAP) && defined(MAP_ANON) && defined(MAP_PRIVATE)
 	if (prekey == NULL)
 		return;
 	munmap(prekey, len);
+#else
+	free(prekey);
+#endif /* HAVE_MMAP et al */
 }
 
 static void